Hydraulic fracturing of reservoirs has been used in the hydrocarbon industry for over fifty years. Efficient production of hydraulically fractured reservoirs requires accurate prediction of the extent and active surface area of fractures or fracture networks that are created and/or activated. Micro-earthquake (MEQ) surveys are often applied to locate the occurrence of fractures and have become critical input to discrete fracture models (DFM). When hydraulic fracturing is used, a proppant is injected alongside the fracturing fluid to hold open the fracture. The proppant is typically a solid material that, when present in a fracture, will hold open the fracture, but which is gas-permeable, allowing for extraction of hydrocarbons at the site of the fracture.
Coupled geomechanical modelling and flow simulation in MEQ derived DFM models are used to predict a stimulated reservoir volume (SRV). MEQ event locations are highly dependent on a velocity model (e.g., a model built to image subsurface locations based on acoustic data) that is used. For example, SRV estimates can change dramatically when velocity models are updated. Even when MEQ event locations are accurate, by themselves MEQ events cannot determine if injected proppant has reached the MEQ event locations or if fractures associated with MEQ events are connected to the well bore. Additionally, existing fractures which may open and accept proppant may not produce a measureable MEQ event. Thus the SRV estimates which are critical for optimal well placement as well as reserve estimates can be extremely uncertain.
Existing systems have attempted to use some Electromagnetic (EM) methods to improve fracture models used in simulation. Single-borehole EM logging and crosswell EM imaging are available, but have limited spatial coverage dictated by well locations. Accordingly, improvements in both EM data acquisition techniques and modeling of subsurface fractures are desirable.